An electron spin double resonance study of x-ray irradiated phenacyl chloride single crystals

Single crystals of phenacyl chloride irradiated at room temperature give rise to an EPR spectrum that has been shown by ENDQR and ELDOR studies to be due to the radical ^CCHCI (I) The EPR spectra are complicated by the appearance of a large number of forbidden lines due to the presence of a chlorine quadrupole interaction similar in magnitude to the proton hyperfine coupling. Spectral assignment is not possible by considering the EPR spectra alone. Although ENDOR spectra are difficult to obtain, it is possible to obtain an ENDOR spectrum along one of the crystal axis that identifies the spectra as due to radical I. Furthermore, rather intense and highly resolved ELDOR spectra are obtained at -60 °C as a function of angle enabling the chlorine and proton magnetic hyperfine tensor components of the -CHCl fragment to be determined as - 15.4, - 8.3, + 45.6 MHz and - 26.5, - 52.5, - 80.0 MHz, respectively. The Q11 cqmponents of the chlorine quadrupole tensor is -11.2 MHz.